Which video player are you using on the computer? Some of them default to muting the audio until you click to unmute and increase the playback level. Try playing another video file on that computer (download and save something from the web) and open it with the same video player to see whether you have sound setting issues with your PC.
Rodger
EOS 1DX M3, 1DX M2, 1DX, 5DS R, M6 Mark II, 1D M2, EOS 650 (film), many lenses, XF400 video
